Far-field optical imaging methods are essential for precise visualization of the dynamics of biomolecules and nanoparticles because they require no contact and make minimal intrusion to the sample. Our research aims to open up new frontiers in chemical and biological discovery through the development and use of novel optical imaging methods, which provide sub-diffraction-limited spatial resolution, high angular resolution, excellent detectability, and nanometer localization precision for single molecules and nanoparticles in biological samples and microfluidic devices.

Single Particle Orientation and Rotational Tracking (SPORT) Techniques. A cell can be conceived as a factory containing a hierarchical network of nanomachines. Fully understanding the working mechanisms of these nanomachines requires knowledge of both translational and rotational dynamics, and their coupling. My laboratory has pioneered the development of optical imaging tools to visualize and understand rotational dynamics in live cells. The SPORT technique offers high spatial, angular, and temporal resolutions simultaneously for visualizing rotational motions of anisotropic plasmonic gold nanorods under a differential interference contrast (DIC) microscope. It has become possible to acquire first-time live-cell observations on many biological events, such as endocytosis and intracellular transport, and provide a significant new dimensionality to the computational efforts in biology. The latest technical advances were chosen for the 2015 Federation of Analytical Chemistry and Spectroscopy Societies (FACSS) Innovation Award.

Probing Cellular Membrane Processes by SPORT. With NIH support, my laboratory is using the SPORT techniques to acquire new fundamental knowledge about the detailed rotational dynamics of cellular membrane processes, such as adhesion, transport, and endocytosis of functionalized nanoparticles, as may be relevant to drug delivery and viral entry. The rotational patterns on cell membranes for functionalized plasmonic gold nanorods are being identified and correlated with their lateral movements and the presence of relevant functional biomolecules tagged with fluorescent proteins. The characteristic rotational motions of cargos during different internalization pathways are being visualized directly, leading to new opportunities for understanding the timing, signaling and chemical and mechanical functions of protein modules involved in different pathways. This research may initiate a shift in the current research paradigm on membrane structure and function by demonstrating the importance of rotational dynamics at the single molecule and nanoparticle level. A thorough understanding of the fundamental motions in evidence will inform about the details of the molecular mechanisms involved in the diffusion of membrane proteins and parallel internalization pathways that will be critical for the better design of antiviral drugs, as well as the development of targeted delivery vehicles and anti-cancer medicines.

In Situ 3D Super-resolution Imaging of Molecular Transport and Catalysis in Nanopores. The emergence of single molecule-based super-localization and super-resolution microscopy imaging techniques have dramatically improved our ability to reveal more detailed molecular dynamics and structural information. However, the current super-resolution chemical imaging techniques still lack several critical abilities, including insufficient axial resolution and the difficulty of imaging more complex 3D nanoscale and mesoscale materials. In seeking to circumvent these limitations, my laboratory is developing novel far-field optical microscopy imaging methods with high sensitivity, superior 3D spatial resolution, and fast temporal resolution for in situ studies of nanoscale and mesoscale materials and processes. These tools are being used to provide new experimental insights on transport in nanoscale confinement, which is fundamentally important in many areas of research and industrial applications, such as chromatographic retention, electrochemical processes, nanofluidics, heterogeneous catalysis, and a host of other systems involving various nanoporous materials.

Microfluidic Devices for High-Fidelity Optical Imaging. Fast developments of optical imaging techniques with high spatial and temporal resolution raise new challenges in the field of microfluidics to fabricate microchannels suitable for highly demanding single molecule and nanoparticle imaging experiments. We introduce novel designs of ultraflat and ultrathin glass/polymer hybrid microdevices to provide almost uncompromised optical imaging quality for on-chip super-localization and super-resolution imaging of single molecules and nanoparticles under a variety of microscopy modes. The high-fidelity (Hi-Fi) optical imaging microfluidic platform allows for time-dependent chemical/biological studies under continuous and controllable external perturbation.